It is generally well known to assemble components (workpieces) together by mechanical instrumentalities such as nuts and bolts, rivets, tabs and slots. For example, with respect to tabs (also known as "lugs" or "pawls") and slots (also known as "slits", "recesses", "grooves" or "indentations"), it is known to assemble blades (also known as "vanes") having tabs on their outer edges to an outer shell (also known as "bowl") of an automotive automatic transmission torque converter impeller or turbine (also known as a "vane wheel", jointly referred to herein as "bowl assemblies") having slots extending into or through its inner surface into which the tabs fit. Similarly, it is known to assemble an inner shroud component (also known as "core tube" or "torus ring") to the inner edges of the vanes by fitting tabs on the inner edges of the vanes through slots extending through the inner shroud component, then bending over the tabs. The use of tabs and slots to assemble vanes to the bowl and shroud of an automatic transmission impeller assembly is shown, for example, in U.S. Pat. No. 3,782,855 (the 1855 patent), and in U.S. Pat. No. 4,868,365 (the '365 patent), incorporated by reference herein. The following paragraphs emphasize certain problems attendant assembling vanes in a bowl of an automatic transmissions.
The '855 patent discloses a vane wheel for fluid couplings or torque converters, especially for motor vehicles. As disclosed therein, a plurality of vanes are disposed between two toroidal surfaces, an outer toroidal surface (e.g., a torque converter shell) and an inner toroidal surface (e.g., a torque converter shroud). As noted in the '855 patent the individual vanes have significant flexibility and, during abrupt changes in transmitted torque, the inner toroidal surface (i.e., the shroud) tends to displace itself angularly (e.g., rotate), vis-a-vis the outer toroidal surface (i.e., the bowl). The solution proposed in this patent is to provide separate and distinct (i.e., from the vanes 12) anti-rotational bracing members (plates 20) extending from the outer toroidal surface to the inner toroidal surface. These plates (20) are fixed by welding or soldering to the toroidal surfaces. In an embodiment of the '855 patent, the anti-rotational bracing members are formed as right-angle bent portions (30) at the ends of certain vanes (12), and these bent portions are advantageously force-fitted between the toroidal surfaces. In a further embodiment, bent portions (30) are formed facing one another on two adjacent vanes (12) and are connected by a bar (35) which is fixed to the bent portions and to the toroidal surfaces by welding, brazing or soldering.
A non-trivial problem in the fabrication and usage of vaned-impellers (or turbines) such as in automotive torque converters (e.g., the impeller assemblies thereof) is leakage (of fluid) occurring between the blades (vanes) and the toroidal surface of the bowl. Generally speaking, leakage will result in decreased fluid dynamic (hydrodynamic) efficiency which, in the context of an automotive torque converter, will translate into reduced gasoline (fuel) efficiency.
U.S. Pat. No. 5,282,362 (the '362 patent) discloses a technique for sealing (reducing leakage) involving the use of elastomeric linings on the core and shell surfaces, proximate the blades. The elastomeric linings are deformed where the blades engage the core and shell surfaces. This localized deformation effects a seal between the core and shell surfaces, which eliminates leakage between the cores and the shells, thereby increasing torque converter efficiency.
Returning to the challenge of affixing a plurality of vanes (blades) to a toroidal surface (especially the outer housing of a torque converter), there has been limited effort in recent years directed to welding the vanes into the bowl. For example, U.S. Pat. No. 4,868,365 (the '365 patent), entitled METHOD FOR WELDING TORQUE CONVERTER BLADES TO A HOUSING USING A LASER WELDING BEAM, discloses forming blades (vanes) with a tab fitted within a recess formed in the impeller housing (bowl) such that the blade stands clear of the adjacent surfaces of the housing by the width of an air gap. A laser beam is directed onto an adjacent surface of the housing a short distance from an edge of the housing adjacent a blade tab to be welded to the housing. A laser beam whose axis is inclined with respect to the recess strikes a surface of the housing adjacent the tab. The welding (e.g., laser) beam is moved parallel to the blade tab so that the blade tab is welded to the housing, without the use of filler material. The housing is rotated to bring successive blade tabs into position for welding.
As is evident, the technique of the "365 patent" amounts to "spot" (localized) welding of the blades to the bowl, and does not address the leakage problem addressed hereinabove. Moreover, in any process, such as those mentioned above, for affixing a plurality of blades to an automatic transmission impeller housing involving the use of slots in the impeller housing, in order to affix a different number or shape of blades to the bowl, or to affix the same (or a different) number of blades to the bowl at a different angle, it is necessary to modify the slot configuration (e.g., number, spacing, angle) of the bowl.
U.S. Pat. No. 5,109,604 (the '604 patent), incorporated by reference herein, discloses a method of assembling a torque converter impeller assembly showing traditional tab/slot assembly of the inner edges of the vanes to a semitoroidal core ring, and a technique of assembling the vanes and core ring as a subassembly to the interior surface of the outer shell (bowl). FIG. 4 of the '604 patent illustrates the process of fixturing (see fixture 39) the vanes for assembly of the core tube (via tabs and slots) to the inner edges of the vanes to fabricate the subassembly. A brazing material is applied to the outer (towards the bowl) edges of the vanes (as well as along the edges of the bent tabs on the inner edges of the vanes). The subassembly of the core ring and vanes, with brazing material applied thereto, is then positioned in the outer shell (bowl). The outer shell, vanes and core ring are then disposed in a brazing oven whereby the brazed metal (e.g., paste) flows along the outer edges of the vanes (as well as along the edges of the inner tabs of the vanes), to securely bond the vanes to the outer shell (as well as to complete the bonding of the core ring to the vanes). The advantages of this technique for assembling the vanes to the bowl, cited in the '604 patent, include:
(a) the vanes need not be aligned with special indentations in the bowl, thereby facilitating the assembly of the torque converter impeller; and
(b) since the outer shell (bowl) does not require indentations (slots), it is not necessary to inventory outer shells by the orientation of the indentations in the outer shell. Outer shells can be used with a variety of vanes and it is easier to change from one vane configuration to another vane configuration.
Irrespective of the particular milieu of affixing vanes to the bowl component of an automatic transmission, brazing is a generally well known technique of joining components (e.g., two articles, two workpieces) to one another and generally involves melting (i.e., causing a thermal reaction in) a brazing material (also referred to as a "filler material") at temperatures of approximately 1000.degree. C. (one thousand degrees Celsius). The brazing material (typically in paste form) may be the same as or different in composition from the material of the to-be-joined components. As distinguished from welding, brazing typically does not involve the melting of the components being joined together, and welding does. (See, e.g., the '365 patent which describes a welding beam melting a component being joined, and subsequent flow of the molten material.) Melting the components being joined together (as in welding) affects the grain orientation of the components, as well as any temper that may have been imparted to the component(s). Irrespective of whether a technique is classified as brazing or welding, the use of high temperatures can cause undesirable distortion, annealing, or the like of one or both of the components (workpieces) being joined together.
Disposing a torque converter impeller in a brazing oven, as disclosed by the '604 patent, is particularly problematic as it will result in "mass" (overall) heating of the components being assembled, as well as in distortion of the components. Such mass heating of the torque converter bowl is detrimental to the metallurgy of the bowl which may, for example, already have been provided with a hardened hub which will lose its temper as a result of such mass heating. Moreover, it is evident that a component heated in an oven to sufficient temperatures to effect brazing will require a significant, and in some cases controlled, cooling-off period.
U.S. Pat. No. 3,673,659 (the '659 patent), entitled METHOD FOR BONDING VANES IN A! TORQUE CONVERTER, describes previous attempts at bonding vanes to a slotless impeller bowl by brazing, using a brazing paste which is a mixture of pulverized copper and alcohol, in an electric furnace. The method described in this patent involves temporarily connecting the vanes to the core ring by spot welding, then fitting this subassembly of vanes/core tube to the bowl. (This pre-fabrication of a subassembly, comprising vanes joined to the core tube for insertion as a unit into the bowl, is analogous to that of the aforementioned '604 patent.) Brazing material, in the form of copper rings (13a, 13b, 13c, 13d), is disposed between flanges (10a, 10b) on the vanes (10) and each of the core tube (11) and the bowl (12). Then, the to-be-brazed assembly is placed in an electric furnace which is filled with a suitable reducing atmosphere and is internally maintained at a temperature ranging from 1,110.degree. C. to 1,130.degree. C. to heat the assembly at a temperature higher than the melting point of the copper rings. The thermal cycle discussed in the "659 patent" is preliminary heating for 18 minutes (until the desired temperature is attained), maintaining the desired temperature for 10 minutes, and slowly cooling down the assembly for 54 minutes--a process taking approximately one and one half hours to achieve the sought after brazing of vanes. There is no suggestion in this patent that the resulting brazed joints are more than localized to the position of the copper rings (e.g., resulting in an analogue of spot-welding the vanes).
Further attention is directed to U.S. Pat. No. 4,833,295 (the '295 patent), entitled WELDING OF PARTS SEPARATED BY A GAP USING A LASER WELDING BEAM, which discloses a related technique for welding together two portions of a cover for a torque converter at an overlap joint using a welding beam.
Another phenomenon attendant automatic transmission bowl assemblies (impellers, turbines) is that the bowl component tends to "balloon" in response to the fluid pressures contained therein. This, of course, exacerbates any pre-existing leakage (i.e., between the vanes and the bowl) problem, since any gap between the vanes and the bowl will grow as the bowl balloons. Additionally, it is intuitively evident that such ballooning of the bowl imposes undesired stresses on the bowl and on any means of joining the vanes to the bowl, and that enhanced bowl stiffness (resistance to ballooning) would be desirable.